1. Field of the Invention
The present invention relates to a control device and a method for operating an internal combustion engine, in which an engine speed of the internal combustion engine is analyzed in order to monitor proper operation.
2. Description of Related Art
Operating methods of the aforementioned type are known and used to detect misfires or leakages of the fuel system, for example. Since hydrocarbons may reach the environment as a result of misfires and the related faulty exhaust gas conditioning, provisions in the law already require the detection of misfires in the operation of an internal combustion engine.
Known methods of the type mentioned in the introduction are based on detecting a sudden decrease in the engine speed due to the lack of combustion in an affected cylinder. In the process, it is typically checked whether the engine speed or its change over time drops below a corresponding applicable threshold value. However, since the measured engine speed of an internal combustion engine is not solely a function of the combustion but of a multitude of other influence variables as well, such as errors in a pulse-generating wheel for measuring the engine speed, crankshaft torsion and vibrations of the drive shaft, the known methods usually process the measured engine speed in such a way that, to begin with, corrections are carried out that compensate for the aforementioned effects, and an engine speed corrected in this manner is then monitored for a sudden decrease.
The correction values required for the compensation are heavily dependent on an operating point of the internal combustion engine, so that a relatively high number of correction values must be stored to monitor a large operating range of the internal combustion engine and, as the case may be, will have to be relearned during operation of the internal combustion engine. This method is very complex and computer-intensive and requires control devices that have a corresponding capacity and sufficiently large memory.